Accounting Policies (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Available-for-sale Equity Securities, Unrealized Gain, After Tax	$ 2,503	$ 0	$ 2,503	$ 0
Net investment gain (loss)	458	7	372	156
Equity securities
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net investment gain (loss)	458	1	368	143
Unrealized Gain (Loss) on Investments	$ 450	$ 0	$ 351	$ 0